Electron tube having a seamed cathode therein



p 19, 1967 D. G. omm 3,343,029

ELECTRON TUBE HAVING A SEAMED CATH'ODE THEREIN Filed April 23, 1965 26 16 -28 F.1. 40 12 4a Halli 4 I N VE N TOR. flak/s 6T Can/e40 United States Patent 3,343,029 ELECTRON TUBE HAVING A SEAMED CATHODE THEREIN Doris G. Conrad, Scotch Plains, N.J., assignor to Radio Corporation of America, a corporation of Delaware Filed Apr. 23, 1965, Ser. No. 450,440 3 Claims. (Cl. '313-356) This invention relates to electron tubes comprising round tubular cathodes having an extending bulge, and particularly to electron tubes having lock seam, right circular cylindrical cathodes.

Lock seam, right circular cylindrical cathodes are fabricated by forming a sheet of metal strip into a round tubular sleeve, overlapping the side edges of the sleeve, and folding over the overlapped edges to form a seam four layers thick. The cathode sleeve is then coated with an electron emissive material.

A problem associated with the use of lock seam cathodes is that the lock seam generally produces a pro-' nounced bulge or flat in the surface of the cathode. During coating of the cathode with electron emissive material, the coating builds up on the flat, thus further accentuating the cathode eccentricity caused by the lock seam. Within an electron tube, the cathode eccentricity causes non-uniform spacing between the cathode and its adjacent electrode. This, as known, is undesirable with respect to providing electron tubes having uniform characteristics from tube to tube. Also, in electron tubes having small electrode spacings, the build-up of coating along the lock seam frequently causes short'circuiting of the tube electrodes.

An object of this invention is to provide a novel means for utilizing right circular cylindrical cathodes having an extending bulge in electron tubes while avoidingthe aforementioned problems.

For achieving this object, a generally right circular cylindrical cathode sleeve is provided having a longitudinally extending bulge and a tab extending outwardly from one end of the sleeve. The tab is positioned at a preselected angle, preferably 90, from the extending bulge. The cathode, along with a grid having two side rods, is assembled into anelectron tube. The cathode tab is disposed at an angle equal to said preselected angle with respect to a line joining the side rods, whereby the bulge is disposed on said line.

As described hereinafter, disposing the bulge on the line joining the side rods places the bulge adjacent a non-active portion of the grid where the presence of the bulge has little or no affect upon the tube characteristics, and wherein the possibility of shorting the bulge against the grid electrode is greatly reduced.

In the drawings:

FIG. 1 is a front elevation an electron tube mount;

FIG. 2 is a plan view of the lower spacer plate of the electron tube mount shown in FIG. 1; and

FIG. 3 is a section on an enlarged scale, partly broken away, along line 3-3 in FIG. 1.

The electron tube mount shown in FIG. 1 comprises a pair of insulator spacer plates 12 and 14 between which is mounted a plurality of electrodes including a cathode 16, a wire wound grid 18, and an anode 20. End portions of the cathode, grid, and anode electrodes extend through apertures in the spacer plates for maintaining the electrodes in proper unright and spaced apart relation.

Cathode 16 is a right circular hollow cylinder having a lock seam 22 (FIG. 3) extending along the length thereof. Lock seam cathodes are well known. Although attempts are made to manufacture the cathode with a perfect partly broken away of right circular cylindrical outer surface, it is found that the lock seam causes an enlargement or bulge in the cathode outer surface. For a cathode coated with an electron emissive material and having an outside diameter of 45 mils, the eccentricity of the cathode at the bulge may be as much as 2 mils. The intended spacing between the cathode and grid electrodes in some electron tubes is as small as 2 mils. Hence the cathode bulge may cause a substantial variation from the desired cathode-to-gn'd spacing, thereby causing substantial variations from the desired electrical characteristics of the electron tubes, and, in some instances, may cause short circuiting between the grid and cathode.

Welded to the outside of the lower end of cathode 16 at an angle of from the lock seam is a flexible tab 24.

Grid 18 comprises a pair of side rods 26 and 28 and a lateral wire helix 30 wound around and between side rods 26, 28. Grid 18 is of the type known in the art as a formed round grid. That is, an arcuate central portion 31 (FIG. 3) of the lateral wire expanse between two end straight portions 32 adjacent the side rods is formed, by known means, to conform to the shape of the cathode.

The lower spacer spacer plate 14 (FIG. 2) has a central aperture 34 for receipt of the lower end of the cathode 16, a pair of apertures 36 on opposite sides of aperture 34 for receipt of the grid side rods 26, 28, and a further pair of apertures 38 for receipt of the anode lower end portions or ears 40. All the apertures lie on a line 42. For facilitating threading of the lower end of cathode 16 and tab 24 through the cathode receiving aperture 34, this aperture is provided with a small enlargement or slot 44 for receipt of tab 24. Slot 44 is disposed 90 from line 42. The upper spacer plate 12 is similar to lower spacer plate 14 except that the cathode receiving aperture therein is not provided with a slot 44.

For providing support and making electricalconnections with the aforementioned electrodes, a stem 48 is provided comprising a header wafer 50, usually of glass, having a plurality of leads 52 extending therethrough. As shown in FIG. 1, the ends of the leads are secured, as by welding, to the side rod 28, the cathode tab 24, and the anode ears 40. Although not shown, an electron tube is provided by adding a heater to the mount 10, enclosing the mount in a suitable envelope, and processing the electron tube, as generally known.

In the assembly of mount 10 the lower end of cathode 16 is first inserted through aperture 34 in lower spacer plate 14, the tab 24 of the cathode being inserted through slot 44. Because of the angular relationships of slot 44 with respect to line 42, and tab 24 with respect to the lock seam 22 of cathode 16, disposing tab 24 through slot 44 automatically disposes the lock seam 22 on or athwart line 42, as shown in FIG. 3. The grid side rods 26 and 28 and the plate ears 40 are then threaded through the apertures in lower spacer plate '14, and the upper spacer plate 12 is then mounted on the upper ends of the cathode, side rods, and anode. The electrode assembly is then mounted on stem 48 by welding the stern leads 52 to the side rod 28 and anode cars 40. Cathode tab 24 is extended towards one of the leads 52 and is welded thereto. This preserves the angular orientation of the cathode and maintains lock seam 22 athwart line 42. Preferably, the cathode sleeve fits snugly within the cathode receiving apertures in spacer plates 12 and 14, and the snug fit further maintains the cathode in angular orientation.

Although not shown, in some instances a cathode is used having an integral tab. That is, the tab is not welded to the outside of the sleeve but is an extension of the sleeve wall. Integral tab cathodes are well known. With such cathodes, the presence of the tab does not increase the outside dimension of the sleeve, as is the case with a welded tab, and a slot 44 in the cathode receiving aperture is not generally used.

For using lock seam integral tab cathodes, the tab is disposed at a preselected angle, preferably 90, With respect to the lock seam. In the assembly of tubes having such integral tab cathodes, the operator angularly orients the cathode by eye using the cathode tab as a guide. That is, the operator angularly disposes the cathode so that the cathode tab is at an angle equal to the preselected angle with respect to the line 42 of spacer plate apertures. This angular disposition of the cathode positions the lock seam athwart the line of the spacer plate cathode and side rod receiving apertures.

By disposing the cathode seam on the line of the spacer plate apertures, two advantages accrue. First, as shown in FIG. 3, the lock seam 22 is disposed in a position where it is a maximum distance from the formed round portions of the grid lateral wires 30. This reduces the possibility of short circuiting the cathode to the grid. Secondly, during operation of the electron tube, the grid 18 is normally operated negative with respect to the cathode. The negative side rods 26, 28 almost completely cut ofi emission oi. electrons from the cathode surface portions opposite the grid side rods. As known, the electrical characteristics of an electron tube are determined substantially by the spacing and physical dimensions of those portions of the electrodes between which electrons flow. Thus, by disposing the lock seam 22 in a region where the cathode is normally cut off, that is, adjacent to the inactive portion of the grid 18, the effects of the lock seam dimensional non-uniformities are greatly reduced.

What is claimed is:

1. An electron tube including:

an otherwise circularly cylindrical cathode having a longitudinally extending bulge along a side portion thereof, said cathode having a tab extending from an end thereof at a preselected angle with respect to said bulge,

a cylindrical grid substantially coaxially surrounding said cathode, said grid having an active portion and an inactive portion, and

said cathode being angularly oriented relative to said grid to dispose said tab at an angle equal to said preselected angle with respect to said inactive portion for disposing said bulge adjacent to said inactive portion.

2. An electron tube comprising:

a pair of spacer plates having a plurality of apertures disposed along a line,

a cathode, and

a grid having a pair of side rods,

the ends of said cathode and side rods being received through said apertures,

said cathode being a right circular cylinder having a longitudinally extending lock seam and a tab extending from one end of said cylinder at a preselected angle with respect to said seam, and said cathode being angularly oriented for disposing said tab at an angle equal to said preselected angle with respect to said line and for disposing said seam on,

said line. 3. An electron tube comprising:

a pair of spacer plates having a plurality of apertures having a tab receiving slot, at an angle equal to said preselected angle with respect to said line, and said tab being aligned with said notch.

References Cited UNITED STATES PATENTS 2,079,057 5/1937 Week 313-340 2,220,909 11/ 1940 Kershaw 3 l335 6 2,263,660 11/1941 Vasselli 313-356 2,266,622 12/1941 Green 313356 JOHN W. HUCKERT, Primary Examiner.

A. I. JAMES, Assistant Examiner. 

1. AN ELECTRON TUBE INCLUDING: AN OTHERWISE CIRCULARLY CYLINDRICAL CATHODE HAVING A LONGITUDINALLY EXTENDING BULGE ALONG A SIDE PORTION THEREOF, SAID CATHODE HAVING A TAB EXTENDING FROM AN END THEREOF AT A PRESELECTED ANGLE WITH RESPECT TO SAID BULGE, A CYLINDRICAL GRID SUBSTANTIALLY COAXIALLY SURROUNDING SAID CATHODE, SAID GRID HAVING AN ACTIVE PORTION AND AN INACTIVE PORTION, AND SAID CATHODE BEING ANGULARLY ORIENTED RELATIVE TO SAID GRID TO DISPOSE SAID TAB AT AN ANGLE EQUAL TO SAID PRESELECTED ANGLE WITH RESPECT TO SAID INACTIVE PORTION FOR DISPOSING SAID BULGE ADJACENT TO SAID INACTIVE PORTION. 